danah boyd has an interesting post on a cultural divide in IM:--those who see it primarily as a 'presence' tool and those who see it primarily as a communications tool:

I don't spend a lot of time conversing on IM, very little in fact. I simply do not have time. But, i am 10 million times more likely to converse with someone who is always-on than someone who just pops up for conversation. The reason is simple - collective signaling of conversational possibility. As an always-on'r, when someone pokes me to talk and i don't have time, i say sorry - can't talk or some equivalent (except in the case of my phone which might appear to be on while i'm doing something but isn't really). I expect the same from my fellow always-on'rs. So, when i'm in the mood to talk to people and they're in the mood to talk to me (or we're equally procrastinating), we come to a consensus and conversation happens.

Now, let's go back to the people who come online just to talk. The problem with this group is that they're unintentionally exerting power. They are declaring their free time by logging on and they're assuming that i am signaling the same thing. But i'm not. This is simply cultural cluelessness. But when they then get upset with me, that's the exertion of power. And this is what has prompted me to change IM accounts or block people in the past. Now, i'm just rude.

Articles I've read indicate that this is an important part of the difference in how teenagers, particularly Japanese teenagers use cell phones and the way the rest of us do--they use them, not necessarily for long conversations--but to 'touch' each other. Longer conversations are negotiated.

I've had people, when I didn't respond to them immediately by instant messenger, call me on the phone--this is the demand approach to communication--I want to talk right now and I demand that you talk to me. It's a stress-added communication style rather than a style that tries to respect both sides of the conversation and it eventually leads to people hiding their presence rather than putting themselves out there where they can interact with people in ways that might work for everyone.